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Electronic TRV Heads and Which for Where?

Postby ericmark » Thu Aug 22, 2019 8:43 am

There are a load of electronic TRV heads all designed to fit on existing TRV's however there is very little given in the adverts on which do what, not wanting to waste money, I have used an expensive one near the wall thermostat an Energenie Mihome which links to the Nest Gen 3 wall thermostat and a much cheaper eqiva Cassellie eQ-3 bluetooth head for most of the others.

Reading the specification sheets that come with these two, it is clear there are many features which are different, and that does not include I am sure many of the software features around anti hysteresis.

So the big question is which and where in the house?

Hive, EvoHome, Tado for example the head tells the thermostat when it needs heat, so the boiler is switched on, Nest links to Energenie but it seems it just sets them all to same temperature, and Energenie has just one button which will activate boost to 20°C all other settings have to be done with a PC, tablet or phone, it does have two sensors one air one water so air temperature is compensated so 20°C target and current means the room is at 20°C.

The eqiva Cassellie eQ-3 bluetooth also has some features, you can set a offset and a window open where if it detects a rapid drop in temperature it assumes a window has been opened and turns off for 1/2 hour very handy when unloading car into kitchen. Unlike the other one, it can only connect to one phone, however it does have a display so all can be set direct on the valve.

Hive has a heat on demand feature, so the TRV head even if the heating is not set to run, can tell the wall thermostat to turn heating on for 1/2 hour, now returning to the eQ-3 it has a boost feature which turns radiator on at 80% for 5 minutes which if the boiler is running will likely heat the room well, as it takes time for a radiator to cool again, but the point is it will only work if the boiler is running.

How they all work will depend on boiler type, home design and living style, basic idea is rooms only heated when required and only to temperature required is I am sure common with all, however how fast is another question, although the Energenie set to 20°C would heat room to 20°C +/- 0.5°C it could take 2 hours to get there, the anti hysteresis software was too good, so 7 am set to 24°C and 8 am set to 20°C worked well getting around the anti hysteresis software, also if the TRV is fitted to return the radiator can become really hot before the valve knows it's being heated, so the lock shield valve setting is important so it does not over shoot.

With a modulating boiler theory the cheap eQ-3 should work great, as boiler modulation controlled by return water temperature, the wall thermostat only stops cycling once warm weather arrives.

However there seems to be some uncertainty on how modulating boilers work, I have seen it written that they work best when on max, also seen it written they don't condense when on max, and depending where you read most economic output is max, midway and min output, maybe this alters boiler to boiler?

As to non modulating, today that means oil fired, the time between cycles is important, plus any run on, I was advised not to put a motorised valve on the domestic hot water as that allowed boiler to cool better and extended boiler life?

As to OpenTherm or other modulating wall thermostat, does it really work better than using the return water temperature? Then so much depends on how a wall thermostat is set, and designed, some have anti hysteresis software built in so start to cycle boiler as set point is reached, clearly not what is wanted for a modulating boiler as it stops it modulating.

As to zone valves, I can't work out why they are fitted, other than the government saying you must, they it seems will defeat all the cleaver controls already talked about. Once TRV's are fitted every room is a zone, so why fit zone valves?

However the point is to start people talking about their TRV heads, how well does yours work? Plumbers and heating engineers may fit 1000's of systems, but they don't use them.

I was told again and again don't fit a TRV in the room with the wall thermostat, in the end I did, and then the system worked, OK the TRV and wall thermostat do need matching, be it manual or automatic, but TRV's in same room as wall thermostat works, special in the hall, it allows a large radiator to re-heat hall after door has been opened, but for it to throttle back before the point where it turns off the wall thermostat so causes rest of house to get cold.

Last professional who fitted central heating for my dad, put a pump on the mains water (breaking the law) and did not adjust one lock shield valve, it was a large firm, all they did was fit central heating, so expected they knew what they were doing, clearly mistaken.

Some are clearly cleaver, but big problem in last house was bay window allowing room temperature to rise quickly if the sun came out in the morning, what was needed was a fast acting TRV, reading the spec, they don't say how quickly they open or close, not very fast as motor can be heard for some time adjusting the valve, but how can one select best when your not told how long it takes?

Fitting the Energenie head resulted in when sun came out room only heated to 24°C not 28°C as had been the case with a wax head, both being set to 20°C. So it was a vast improvement, the electronic head turned the radiator off quicker. As to if the cheaper eQ-3 would have done the same I don't know, not done a winter with them fitted.

So thoughts and experiences please, told the Drayton Wiser works well, the Danfoss Eco electronic head is a stand alone bluetooth at £35 when my eQ-3 cost £15 each. The Terrier i30 also stand alone, so big question do we need linked to room thermostat for all rooms, or just some rooms? With a price range of £10 to £65 and 14 radiators that's a lot of money to fit linked to every radiator.
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